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Chapter 20 . By: Kate Crowe . Section 20-1. WHAT ARE THE CAUSES AND EFFECTS OF WATER POLLUTION?. Water pollution comes from point and nonpoint sources.

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Water pollution is any change in water quality that can harm living organisms or make the water unfit for human uses such as irrigation and recreation.

Water pollution can come from a single (point) source, or from a larger, more dispersed (nonpoint) source.

Point sources discharge pollutants into bodies of surface water at specific locations through drain pipes, ditches, or sewer lines.

Nonpoint sources are broad and diffuse areas, rather than points, from which pollutants enter bodies of surface water or air.

Agricultural activities are by far the leading cause of water pollution. Sediment eroded from agricultural lands is the most common pollutants.

Industrial facilities, which emit a variety of harmful inorganic and organic chemicals, are a second major source of water pollution. A growing problem of great concern is that of coal ash, an indestructible waste created by the burning of coal in power plants.

One of the major water pollution problems that we face is exposure to infectious disease organisms through drinking water contaminated with human and animal wastes.

Cleaning up water supplies has helped to control some of these diseases.

In 2010, the United Nations reported that each year, unsafe water kills more people than war and all other forms of violence combined.

The WHO has estimated, more than 1.6 million people die every year from largely preventable waterborne infectious diseases that they get by drinking contaminated water or by not having enough clean water for adequate hygiene. This adds up to an average of nearly 4,400 premature deaths a day, 90% of them in children younger than age 5.

Laws enacted in the 1970s to control water pollution have greatly increased the number and quality of wastewater treatment plants in the United States and in most other more-developed countries.

One success story is the cleanup of the U.S. state of Ohio’s Cuyahoga River. It was so polluted that it caught fire several times and, in 1969, was photographed while burning as it flowed through the city of Cleveland toward Lake Erie, one of the Great Lakes.

The highly publicized image of this combustible river prompted elected officials to enact laws that limited the discharge of industrial wastes into the river and into local sewage systems, and provided funds to upgrade sewage treatment facilities.

Fish kills and drinking water contamination still occur occasionally in some of the rivers and lakes of more-developed countries.

Eutrophication is the name given to the natural nutrient enrichment of a shallow lake, estuary, or slow-moving stream. It is caused mostly by runoff of plant nutrients such as nitrates and phosphates from surrounding land.

An oligotrophic lake is low in nutrients and its water is clear

Near urban or agricultural areas, human activities can greatly accelerate the input of plant nutrients to a lake… a process called cultural eutrophication.

There are several ways to clean up lakes suffering from cultural eutrophication.

They include mechanically removing excess weeds, controlling undesirable plant growth with herbicides and algaecides, and pumping air into lakes and reservoirs to prevent oxygen depletion, all of which are expensive and energy-intensive methods.

On a global scale, we do not know much about ground- water pollution because few countries go to the great expense of locating, tracking, and testing aquifers.

Groundwater provides about 70% of China’s drink- ing water.

Groundwater used as a source of drinking water can also be contaminated with nitrate ions (NO3-), especially in agricultural areas where nitrates in fertilizer can leach into groundwater.

Nitrite ions (NO2-) in the stomach, colon, and bladder can convert some of the nitrate ions in drinking water to organic compounds that have been shown in tests to cause cancer in more than 40 animal species.

By 2008, the EPA had completed the cleanup of about 357,000 of the more than 479,000 underground tanks in the United States that were leaking gasoline, diesel fuel, home heating oil, or toxic solvents into groundwater.

Coastal areas—especially wetlands, estuaries, coral reefs, and mangrove swamps—bear the brunt of our enormous inputs of pollutants and wastes into the ocean

According to a 2006 State of the Marine Environment study by the UN Environment Program (UNEP), an estimated 80% of marine pollution originates on land (Concept 20-4a), and this percentage could rise significantly by 2050 if coastal populations double as projected.

In deeper waters, the oceans can dilute, disperse, and degrade large amounts of raw sewage and other types of degradable pollutants.

Some scientists suggest that it is safer to dump sewage sludge, toxic mining wastes, and most other harmful wastes into the deep ocean than to bury them on land or burn them in incinerators.

Other scientists disagree, pointing out that we know less about the deep ocean than we do about the moon.

Crude petroleum (oil as it comes out of the ground) and refined petroleum (fuel oil, diesel, gasoline, and other processed petroleum products) reach the ocean from a number of sources and become highly disruptive pollutants.

Tanker accidents and blowouts at offshore drilling rigs (when oil and natural gas escape under high pressure from a borehole in the ocean floor) get most of the publicity because of their high visibility.

In April of 2010, such a blowout occurred in the Gulf of Mexico.

But studies show that the largest source of ocean pollution from oil is urban and industrial runoff from land, much of it from leaks in pipelines and oil-handling facilities.

Volatile organic hydrocarbons in oil kill many aquatic organisms immediately upon contact. Other chemicals in oil form tarlike globs that float on the surface and coat the feathers of seabirds and the fur of marine mammals.

In rural and suburban areas with suitable soils, sew- age from each house usually is discharged into a septic tank with a large drainage field.

In urban areas in the United States and other more- developed countries, most waterborne wastes from homes, businesses, and storm runoff flow through a network of sewer pipes to wastewater or sewage treatment plants.

Raw sewage reaching a treatment plant typically undergoes one or two levels of wastewater treatment. The first is primary sewage treatment—a physical process that uses screens and a grit tank to remove large floating objects and to allow solids such as sand and rock to settle out. Then the waste stream flows into a primary settling tank where suspended solids settle out as sludge.

By itself, primary treatment removes about 60% of the suspended solids and 30–40% of the oxygen-demanding organic wastes from sewage.

The second level is secondary sewage treatment—a biological process in which aerobic bacteria remove as much as 90% of dissolved and biodegradable, oxygen-demanding organic wastes.

A third level of cleanup, advanced or tertiary sewage treatment, uses a series of specialized chemical and physical processes to remove specific pollutants left in the water after primary and secondary treatment.

Federal law in the United States requires primary and secondary treatment for all municipal sewage treatment plants, but exemptions from secondary treatment are possible when the cost of installing such treatment poses an excessive financial burden on towns and cities.